Method and apparatus for resecting a distal femur and a proximal tibia in preparation for implanting a partial knee prosthesis

ABSTRACT

A method of resecting a proximal tibia and distal femur for implanting a partial knee prosthesis uses a resecting kit which includes multiple spacers, each of which has a different spacing dimension. A surgeon selects the appropriate spacer with the amount of correction desired to align the patient&#39;s leg and installs the spacer with the spacing dimension between the distal femur and proximal tibia which is to receive the partial knee prosthesis. The spacers have projecting stems, upon which a resector is installed. The resector is then aligned with the axis selected by the surgeon according to known methods, and is pinned to the femur and proximal tibia. A distal femoral cut is then made in the femur after which the resector is removed while leaving at least two of the pins in place, the pins being headless pins. A second resector is then installed on the pins to effect the required cut of the tibia. Additional cuts are made in the femur according to known procedures, and the femoral and tibial prostheses are then installed, according to known procedures.

TECHNICAL FIELD

[0001] This invention relates to a method and apparatus for resecting adistal femur and a proximal tibia in preparation for implanting apartial knee prosthesis.

BACKGROUND OF THE INVENTION

[0002] Partial knee replacement surgery has become relatively common,and according to traditional practice, requires a relatively largeincision in the patient in order to realign the patient's leg, removeany diseased bone and cartilage, and provide a proper surface forengagement with the tibial and femoral prostheses which must mate toform the partial knee replacement. Such large and complicated incisionsincrease surgical time and risk and also lengthen patient recovery.Accordingly, more recently minimally invasive techniques have becomeavailable, which greatly reduce the size of the required incision, thusproviding more rapid healing and recovery for the patient. Theinstruments used in minimally invasive surgery clearly must berelatively small and are preferably uncomplicated, due to the spaceconstraints within the knee. Further, these instruments must permitalignment of the knee and the proper preparation of the implant surfacesin order to receive and retain the prostheses.

[0003] When a patient's knee deteriorates, cartilage wears away, and thepatient becomes bow-legged (or knock-kneed), depending upon which sideof the knee is diseased. Accordingly, instruments must be used to resetthe spacing between the distal femur and proximal tibia receiving thepartial knee implant, to correct bow-leggedness and the patient'sknock-knees. Overcorrection must be avoided, in order to avoid wear (andeventual deterioration) of the side of the knee not receiving thepartial knee prosthesis.

SUMMARY OF THE INVENTION

[0004] The present invention provides a resecting kit which includesmultiple spacers, each of which has a different spacing dimension. Asurgeon selects the appropriate spacer with the amount of correctiondesired to align the patient's leg and installs the spacer with thespacing dimension between the distal femur and proximal tibia on theside of the knee which is to receive the partial knee prosthesis. Thespacers have projecting stems, upon which a resector is installed insuch a way that the resector may pivot around the stem. The resector isthen aligned with the axis selected by the surgeon according to knownmethods, and is pinned to the femur and proximal tibia. A cut is thenmade in the femur after which the resector is removed while leaving thetibial pins in place, the pins being headless pins. A second resector isthen installed on the pins to effect the required cut of the tibia.Other cuts are made in the femur according to known procedures, and theprostheses are then installed according to known procedures.

[0005] Accordingly, since they are relatively small, the spacers arerelatively easy to install between the proximal tibia and distal femur.The spacers include a recess to clear the anterior tibial rise, suchthat the spacer is fully engaged both with the corresponding condyle andthe tibial plateau where the prostheses are to be implanted. Since thespacers have no moving parts, minimal manipulation of the instrumentswithin the saggital plane is required.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a sagittal view of a partial knee prosthesis implantedon the distal femur and proximal tibia of a patient;

[0007] FIGS. 2-5 are side views of spacers used in the surgery resectingthe proximal tibia and distal femur to accommodate implantation of theimplant illustrated in FIG. 1;

[0008]FIG. 6 is a sagittal view illustrating one of the spacersillustrated in FIGS. 2-5 installed between the distal femur and proximaltibia of a patient undergoing knee replacement surgery;

[0009]FIG. 7 is a posterior view taken along line 7-7 of FIG. 6;

[0010]FIG. 8 is a sagittal view similar to FIG. 6 but illustrating aresector installed on the spacer illustrated in FIG. 6;

[0011]FIG. 9 is an anterior view taken substantially along lines 9-9 ofFIG. 8;

[0012]FIGS. 10 and 11 are views similar to FIGS. 8 and 9 respectivelybut illustrating an alignment tower installed on the resectorillustrated in FIGS. 8 and 9;

[0013]FIGS. 12 and 13 are views similar to FIGS. 10 and 11, butillustrating an alignment rod installed on the alignment tower;

[0014]FIGS. 14 and 15 are views similar to FIGS. 8 and 9, butillustrating the manner in which the distal femur is resected using theresection kit in the present invention;

[0015]FIGS. 16 and 17 are views similar to FIGS. 14 and 15, butillustrating another resector mounted on the spacer and furtherillustrating the manner in which the resection is performed;

[0016]FIGS. 18 and 19 are views similar to FIGS. 16 and 17 butillustrating the completed tibial cut and distal femoral cut.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] As discussed above, the present invention relates to a method andapparatus for resecting a femur and tibia and for implanting a partialknee prosthesis, the resection being effected by using a resecting kit.The resecting kit includes a set of multiple spacers each havingdifferent spacing dimensions to permit the surgeon to adjust the spacingbetween the proximal tibia and distal femur at the side of the kneewhich the prosthesis is to be implanted, a pair of resectors for guidingresectioning of the tibia and femur, and other instruments for aligningthe leg and preparing the knee for implantation of the partial kneeprosthesis.

[0018] Referring now to the drawings, a partial knee prosthesisgenerally indicated by the numeral 10 includes a femoral prosthesis 12and a tibial prosthesis 14. Femoral prosthesis 12 is implanted upon thedistal femur 16, and the tibial prosthesis 14 implanted on the proximaltibial 18. As seen is FIGS. 7 and 9, the femur terminates in condyles 20and 22. Since the prosthesis 10 may be used to replace either thelateral or medial condyle of the patient, femur 16 and proximal tibia 18may represent either the right or left leg of the patient. The proximaltibia 18 terminates in a tibial plateau 24 bounded in part by theanterior tibial rise 26. In order to effect proper implantation of theprosthesis, a portion of the tibial plateau must be resected to providea flat surface 28, which must be drilled in order to accommodateimplantation of tibial prosthesis 14, which is then cemented into place.The distal femur must be resected to provide a distal femoral cutforming a surface 30, a posterior chamfer femoral cut forming a surface32, and a posterior femoral cut forming a surface 34. Femoral prosthesis12 includes anchors (not shown) which are received within holes drilledin one or more of the surfaces 30, 32 and 34 The present inventionrelates to a method and apparatus for effecting the resections formingthe surfaces 28 and 30. Surfaces 32 and 34 are resected after theresections forming the surfaces 28 and 30 are effected. The cutsresulting in surfaces 32 and 34 are made in a conventional manner, suchas by temporarily installing a drilling and cutting guide in the priorart on the surface 30 and then making the cuts necessary to form thesurfaces 32 and 34.

[0019] To insure an acceptable result, it is desirable that the surfaces28 and 30 held to as nearly parallel as possible in the lateral/medialplane, and that the surfaces 28, 30 diverge from each other about 6degrees-8 degrees in the anterior to posterior plane. It is alsonecessary to align the patient's leg to correct bow-leggedness or thepatient's knock-knees. If the diseased side of the joint is the medialside, the deterioration and the cartilage and any subsequentdeterioration of the bone will cause the distance between thecorresponding condyle and corresponding portion of the tibial plateau tonarrow, resulting in the patient becoming bow-legged. On the other hand,if the diseased portion of the joint is on the lateral side, the patientbecomes knock-kneed. In any case, it is necessary during surgery toeffect implantation of the prosthesis 10 to realign the patient's legand correct the bow-leggedness and/or knock-knees. The method andresection kit of the present invention permits the patient's leg to bestraightened without over-correcting, since any over-correction willresult in increased wear on the other side of the joint. Furthermore,the method and kit according to the present invention assures properalignment of the surfaces 28 and 30.

[0020] After the joint has been opened by an incision of about two tothree inches in length, the surgeon selects one of the spacers 36A-Dillustrated in FIGS. 2-5 which the surgeon judges will provide theproper spacing between the distal femur 16 and proximal tibia 18 tocorrect the alignment of the patient's leg. In practice, many morespacers having different spacing dimensions will be provided; thespacers have been illustrated in FIGS. 2-5 for illustrative purposesonly. Each of the spacers 36A-D include a stem 38 and an arm 40extending from the stem. Small spacer 36A includes an arm 40 whichincludes a pair or opposed, substantially flat, parallel surfaces 42,44. The spacing dimension of spacer 36A is the distance between thesurfaces 42 and 44. Each of the remaining spacers 36B-D include an arm40A-D having a substantial flat upper surface 42A with a bump 46projecting from the surface 44. Each of the bumps 46 are defined by acurved surface 48 for a purpose described hereinafter. The spacingdimensions in each of the spacers 36B-D is the distance between theupper surface 42 and the maximum dimension of the bump 46. Curvedsurface 48 of the bump 46 cooperates with the surface 44 and transverseend surface 50 of the stem 38 to define a recess 52 therebetween.Transversely spaced, longitudinally extending keels 54 are provided onthe bumps 46 (see FIG. 7).

[0021] After the patient's knee has been opened by the surgeon, thesurgeon selects one of the spacers 36 which the surgeon judges willcorrect the patient's knock-knees or bow-leggedness and properly alignthe patient's leg. The surgeon manipulates the bump 46 (or the flat armof spacer 36A) of the selected spacer over the anterior tibial rise 26so that the anterior tibial rise 26 is received within the recess 52 ofthe spacer, the curved surface 48 engages the tibial plateau 24, and theupper flat surface 42 engages the contoured surface 55 of the condyle 20at its closest approach to the tibial plateau 24. The keels 54 resistmovement of the spacer 36 in the lateral-medial direction, but permitmovement in the anterior-posterior direction to permit installation ofthe spacer such that the spacer separates the joint to correct theaforementioned alignment of the patient's leg. When the spacer isproperly installed with the upper surface 42 engaging the contouredsurface 55 at its, closest approach to the tibial plateau and with thecurved surface 48 engaged with the tibial plateau, the surgeon thenmakes a judgment as to whether the patient's leg is properly aligned. Ifthe surgeon decides that a different spacer is needed, the surgeonremoves the first selected spacer and selects another spacer forinstallation between the distal femur 16 and proximal tibia 18. It willbe noted that stem 38 of the selected spacer projects from the joint.

[0022] The surgeon then installs resector 56 on the stem 38 (FIGS. 8 and9). The resector 56 includes a cylindrical aperture 58 slidably androtatably engages the stem 38 to permit the resector 56 to pivot aboutthe stem 38. The resector 56 further includes a slot 60 which is adaptedto receive the blade of a saw that will effect cutting of the condyle20. The resector 56 includes multiple apertures 62, 64, 66, 68, and 70,which are adapted to receive pins which will be hereinafter described.Furthermore, the resector 58 includes a pair of opposed, parallel sideedges 72, 74.

[0023] After the resector is installed on the stem 38, an alignmenttower generally indicated by the numeral 76 (FIGS. 10 and 11) isinstalled on the resector 56. The tower 76 includes a bifurcated end 78including arms 80 that slidably engage the opposite side edges 72, 74 ofthe resector 56. The opposite end of the alignment tower 76 carries acylinder 82, which projects transversely with respect to the alignmenttower 76. A longitudinal opening 83 in alignment tower 76 receives theportion of stem 38 projecting from resector 56. Cylinder 82 defines anopening 84 extending transversely with respect to the alignment tower 76which receives a longitudinally extending alignment rod 86. It is notedthat, the side edges 72, 74 of resector 56 are perpendicular to the slot60 in the resector 56, since the alignment tower 76 maintains thealignment rod 86 parallel to the side edges 72, 74, the axis of thealignment rod 86 will accordingly also be perpendicular to the slot 60.According to well-known techniques, the surgeon manipulates thealignment rod 86, which extends the entire length of the tibia, untilthe alignment rod 86 extends along an axis desired by the surgeon andwhich is chosen according to the surgeon's judgment and experience. Inmost cases, however, the selected axis will approximate the mechanicalaxis of the tibia. It will be noted that because of the curved surface48 of the bump 46, the surgeon may rotate the spacer in the sagittalplane to permit the rod 86 to clear any obstacles, such as anyprojecting portions of the patient's leg or ankle.

[0024] After the surgeon is satisfied with the alignment of the resector56, headed or headless pins are installed in aperture 62 and headlesspins are installed into a selected pair of apertures 64-70. Asillustrated in FIGS. 14 and 15, pin 88 is installed in aperture 62 andpins 90 and 92 are installed in the apertures 64 and 68. The pins 88-92are installed and secured in holes drilled in the distal femur andproximal tibia to thereby secure the resector 56 in place. As discussedabove, the slot 60 of resector 56 will be perpendicular to the axisselected by the physician. After the resector 56 is pinned, thealignment rod 86 and alignment tower 76 are removed. A threaded opening93 is provided which receives an appropriate threaded rod of a tool usedto extract the alignment tower 76. A blade 94 of a conventional surgicalsaw is installed in the slot 60 and effects cutting of the condyle 20 toform the surface 30. Since the saw is guided by the slot 60, surface 30will also be perpendicular to the axis selected by the physician.

[0025] After the surface 30 is cut, the pin 88 is removed, but the pins90 and 92 are left in place. Since the pins 90, 92 are headless pins,the resector 56 may be pulled off of the pins by use of appropriateclamping tool (not shown) engaging the side edges 72, 74 so that theresector 56 may be pulled off of the pins 90, 92. After the surgeon hasremoved the resector 56, a second resector 96 is installed on the pins90 and 92, care having been taken not to disturb the pins 90 and 92 inany way during the removal of the resector 56 and installation of theresector 96. The resector 96 is provided with a first set of apertures98A, 98B, a second set of apertures 100A, 100B, a third set of apertures102A, 102B, and a fourth set of apertures (through which the pins 90 and92 extend as illustrated in FIGS. 16-17) 104A and 104B. Each of theaperture sets are spaced a distance to conform with the spacing betweenthe pins 90 and 92, as established by use of the resector 56 asdescribed above. The multiple sets of apertures are provided so that thesurgeon may select the distance between the tibial cut and the distalfemoral cut. The resector 96 is also provided with a slot 106. Theresector is installed on the pins 90 and 92 and since the resector 96has been designed with the slot 106 in a pre-established relationshipwith respect to the slot 60, the cut formed by the saw blade 108 throughthe slot 106 has the same relationship to the distal femoral cut 32.That is, the tibial cut formed by saw blade 108 in slot 106 in theresector 96 will be parallel to the horizontal femoral of surface 32 inthe laterally-medial plane, and will have the proper diverging angle inthe anterior posterior plane. After the tibial surface 28 is formed, theresector 96 is removed from the pins 90 and 92. The aforementionedfixture (not shown) is mounted on the surface 32 to guide resection ofthe surfaces 32, 34, and to drill the necessary apertures (not shown) tomount the femoral prosthesis 30. Similarly, a template (not shown) isused to drill the necessary mounting holes in the tibial surface 28. Theprostheses 12 and 14 can then be installed according to knownprocedures.

[0026] Referring now to the embodiment of FIGS. 20 and 21, elements thesame or substantially the same as those in the embodiment of FIGS. 1-19retain the same reference numeral. A spacer generally indicated by thenumeral 110 for setting the spacing between the distal femur andproximal tibia has been selected by the surgeon from a set of spacerssimilar to the set illustrated in FIGS. 2-5. However, the stem 38 of thespacers illustrated in FIGS. 2-5 has been replaced on the spacer 110 bya stem 112 having flats 114, 116 on opposite sides thereof. Similarly,the resector 56 of the embodiment of FIGS. 1-19 has been replaced with aresector 118 in the embodiment of FIGS. 20 and 21, which differs fromthe resector 56 only in that the aperture 58 of resector 56 has beenreplaced in resector 118 with an aperture 120 which is shapedcomplementary to the stem 112 (that is, with opposite flats 122, 124) sothat the stem 112 is slidably received in the aperture 120 but isprevented from rotating relative thereto.

[0027] Accordingly, when the alignment tower 76 is installed on theresector 118 (in exactly the same manner as described above with respectto the resector 56), the resector 118 will not rotate relative to thestem during the alignment procedure but instead will pivot the spacer110 relative the distal femur and proximal tibia. Since the resector 118is not rotated relative to the spacer, the surgeon is assured that thecut made by use of the resector 118 is at a predetermined distance fromthe upper surface 42 of the spacer and is parallel thereto, although thespacing between the distal femur and proximal tibia will be slightlydifferent from that initially established by installation of the spacer110. Some surgeons prefer to assure that the size of the cut isconfirmed by the resector, even if the spacing between the bones may beaffected slightly; accordingly, these surgeons may prefer to use thespacer 110 and resector 118.

1. Method of resecting a distal femur and a proximal tibia inpreparation for implanting a partial knee prosthesis comprising thesteps of installing a spacer having a fixed spacing dimension betweenthe distal femur and proximal tibia to establish a gap of known widththerebetween, said spacer having a projecting stem, mounting a resectoron said stem, aligning said resector along a selected axis representedby an alignment rod extending from said resector, pinning said resectorto both said distal femur and proximal tibia using multiple pins toprevent relative movement of said resector with respect to both saiddistal femur and proximal tibia, and using said resector to guideresection of one of said distal femur and proximal tibia.
 2. Method ofresecting as claimed in claim 1, wherein said method includes the stepof selecting said spacer from a set of multiple spacers each having adifferent fixed spacing dimension.
 3. Method of resecting as claimed inclaim 1, wherein said fixed spacing dimension is defined by a bump onsaid spacer having a curved outer edge, said method including the stepof rotating said spacer about said curved outer edge to permit saidalignment rod to manipulated over obstructions.
 4. Method of resectingas claimed in claim 3, wherein said proximal tibia terminates in atibial plateau and said distal femur terminates in a condyle having acontoured distal surface defining said gap established by said spacer,said spacer having a flat surface opposite said bump, said methodincluding the step of maintaining engagement of said flat surface withsaid area as said spacer is installed between said distal femur andproximal tibia.
 5. Method of resecting as claimed in claim 1, whereinsaid spacer includes an arm extending axially from said stem, said fixedspacing dimension being defined by a bump extending from one side ofsaid arm and a substantially flat surface on the other side of said armopposite said bump, said method including the step of inserting said armbetween said distal femur and proximal tibia while maintaining said flatsurface in engagement with said distal femur and the bump in engagementwith said proximal tibia.
 6. Method of resecting as claimed in claim 5,wherein said bump is defined by a curved outer edge, said methodincluding the step of rotating said spacer about said curved outer edgeto permit said alignment rod to manipulated over obstructions.
 7. Methodof resecting as claimed in claim 5, wherein said proximal tibiaterminates in a tibial plateau and said distal femur terminates in acondyle having a contoured distal surface defining said gap establishedby said spacer, said method including the step of maintaining saidcurved outer edge in engagement with said tibial plateau and saidsubstantially flat surface in engagement with said contoured distalsurface as said spacer is rotated about said curved outer edge. 8.Method of resecting as claimed in claim 1, wherein said proximal tibiaterminates in a tibial plateau bounded by an anterior tibial rise, andsaid distal femur terminates in a condyle having a contoured distalsurface defining said gap established by said spacer, said spacerincluding an arm extending axially from said stem, said fixed spacingdimension is defined by a bump extending from one side of said arm and asubstantially flat surface on the other side of said arm opposite saidbump, said step of installing said spacer including the steps of slidingthe bump over the anterior tibial rise while maintaining said flatsurface in engagement with said contoured distal surface.
 9. Method ofresecting as claimed in claim 8, wherein said arm defines a recessbetween said bump and said stem, said method including the step ofpermitting said anterior tibial rise to be received within said recesswhen the spacer is installed in said gap.
 10. Method of resecting asclaimed in claim 1, wherein said proximal tibia terminates in a tibialplateau bounded by an anterior tibial rise, and said distal femurterminates in a condyle having a contoured distal surface defining saidgap established by said spacer, said spacer including an arm extendingaxially from said stem, said fixed spacing dimension being defined by abump extending from one side of said arm and cooperating with said stemto define a recess therebetween, said method including the steps ofengaging said bump with the tibial plateau, receiving said tibial risein said recess, and engaging said arm with said contoured distalsurface.
 11. Method of resecting as claimed in claim 1, wherein saidmethod includes the step of using a second resector to resect the otherof said distal femur and proximal tibia.
 12. Method of resecting asclaimed in claim 11, wherein said method includes the steps of removingsaid first-mentioned resector from said pins after resecting said one ofsaid distal femur and proximal tibia without changing the position of atleast two of said pins, and installing said second resector on saidpins, whereby the orientation of the cuts in the distal femur andproximal tibia relative to one another is maintained by the unchangedposition of said pins.
 13. Method of resecting as claimed in claim 12,wherein said second resector includes multiple sets of apertures forreceiving said pins, whereby the distance between said cuts may bevaried while maintaining the orientation of the cuts relative to oneanother.
 14. Method of resecting as claimed in claim 1, wherein saidresector is aligned by rotating said resector relative to said stem. 15.Method of resecting as claimed in claim 1, wherein said resector isaligned by pivoting the resector and the spacer as a unit, said resectorbeing secured against rotation relative to said spacer.
 16. Resectingkit for resecting a distal femur and a proximal tibia in preparation forimplanting a partial knee prosthesis comprising a set of multiplespacers each having a different fixed spacing dimension whereby a spacerhaving the desired spacing dimension may be selected and installedbetween the distal femur and proximal tibia to establish a desiredspacing therebetween, and resecting means mountable on said spacers forresecting said distal femur and proximal tibia.
 17. Resecting kit asclaimed in claim 16, wherein each of said spacers includes a projectingstem, said resecting means including a resector having an aperturepivotally mounted on said stem and multiple pins for securing saidresector, said resector guiding resection of one of said distal femurand proximal tibia.
 18. Resecting kit as claimed in claim 17, whereinsaid resecting means includes a second resector, said pins beingheadless to permit removal of said first-mentioned resector andinstallation of said second resector on said pins whereby the pinsmaintain the relative orientation of said resectors to permit resectionof the other of said distal femur and proximal tibia.
 19. Resecting kitas claimed in claim 16, wherein each of said spacers includes an armextending between said proximal tibia and distal femur and a stem, saidarm extending from said stem, said stem projecting from between saiddistal femur and proximal tibia, said resecting means being mounted onsaid stem.
 20. Resecting kit as claimed in claim 19, wherein the arm ofat least one of said spacers is a substantially flat blade havingopposite substantially flat surfaces for engagement with said proximaltibia and distal femur respectively, said spacing dimension being thethickness of said blade between said substantially flat surfaces. 21.Resecting kit as claimed in claim 19, wherein the distal femurterminates in a pair of condyles and the proximal tibia terminates in atibial plateau circumscribed in part by an anterior tibial rise, saidarm including a bump on one side thereof for engagement with the tibialplateau and a surface opposite said bump for engagement with acorresponding one of said condyles.
 22. Resecting kit as claimed inclaim 21, wherein said surface opposite said bump is a substantiallyflat surface.
 23. Resecting kit as claimed in claim 21, wherein said armdefines a recess between said stem and said bump, said recess receivingthe anterior tibial rise when the spacer is installed with the bumpengaging the tibial plateau.
 24. Resecting kit as claimed in claim 23,wherein said stem terminates in a transverse surface defining one edgeof said recess.
 25. Resecting kit as claimed in claim 21, wherein saidbump is defined by a curved outer edge to permit limited rotation ofsaid spacer about said curved outer edge in response to movement of thestem in a sagittal plane.
 26. Resecting kit as claimed in claim 25,wherein said bump includes transversely spaced keels to resist movementof the spacer in a lateral-medial plane when the spacer is installedbetween the one condyle and said tibial plateau.
 27. Spacer for use inorthopedic surgery for establishing a known spacing dimension betweencontiguous ends of skeletal members, comprising a stem projecting frombetween said skeletal members when the spacer is installed therebetweenand an arm extending from said stem, said arm having a bump on one sidethereof and an engagement surface on the other side thereof, saidspacing dimension being the distance between the engagement surface andthe region of said bump of maximum distance from said engagementsurface.
 28. Spacer for use in orthopedic surgery as claimed in claim27, wherein said bump is defined by a curved outer edge to permitlimited rotation of said spacer about said curved outer edge in responseto movement of the stem.
 29. Spacer for use in orthopedic surgery asclaimed in claim 27, wherein said bump includes transversely spacedkeels to resist transverse movement of the spacer when the latter isinstalled between skeletal members.
 30. Spacer for use in orthopedicsurgery as claimed in claim 27, wherein said arm defines a recessbetween said stem and said bump.
 31. Spacer for use in orthopedicsurgery as claimed in claim 30, wherein said stem terminates in atransverse surface defining one edge of said recess.
 32. Spacer for usein orthopedic surgery as claimed in claim 31, wherein said engagementsurface opposite said bump is a substantially flat surface.
 33. Spacerfor use in orthopedic surgery as claimed in claim 29, wherein said stemis substantially cylindrical.
 34. Spacer for use in orthopedic surgeryas claimed in claim 29, wherein said stem includes flats on oppositesides of the stem.
 35. Spacer kit for use in orthopedic surgery forestablishing a known spacing dimension between contiguous ends ofskeletal members, comprising multiple spacers each having a knownspacing dimension, said spacers each having an arm for installationbetween said skeletal members and a stem extending from said arm, atleast some of said spacers having a stem and an arm extending from saidstem, said arm having a bump on one side thereof and an engagementsurface on the other side thereof, said spacing dimension being thedistance between the engagement surface and the region of said bump ofmaximum distance from said engagement surface, said bump having a heightdifferent for each of said spacers whereby a selected spacer may be usedto establish a corresponding spacing dimension.
 36. Spacing kit asclaimed in claim 35, wherein the arm of at least one of said spacers isa substantially flat blade having opposite substantially flat surfaces,said spacing dimension being the thickness of said blade between saidsubstantially flat surfaces.
 37. Spacing kit as claimed in claim 36,wherein each bump is defined by a curved outer edge to permit limitedrotation of said spacer about said curved outer edge in response tomovement of the stem.
 38. Spacing kit as claimed in claim 36, whereineach bump includes transversely spaced keels to resist transversemovement of the spacer when the latter is installed between skeletalmembers.
 39. Spacing kit as claimed in claim 36, wherein each bumpcooperates with its arm and stem to define a recess therebetween. 40.Spacing kit as claimed in claim 35, wherein each bump is defined by acurved outer edge to permit limited rotation of said spacer about saidcurved outer edge in response to movement of the stem
 41. Spacing kit asclaimed in claim 36, wherein each bump cooperates with its arm and stemto define a recess therebetween.